SOUTHEASTERN GEOLOGY V. 39, No.3 & 4, October 2000, p.p. 223·241

REGOLITH IN THE PIEDMONT UPLAND SECTION, PIEDMONT PROVINCE, YORK, LANCASTER, AND CHESTER COUNTIES, SOUTHEASTERN PENNSYLVANIA

W.D.SEVON PePennsylvania Geological Survey p. O. Box 8453 Harrisburg, PA 17105-8453

ABSTRACT ~80KM

Regolith has been mapped in the Pied­ mont Upland Section of the Piedmont Prov­ ince in York, Lancaster, and Chester Counties, southeastern Pennsylvania. The Pennsylvania Piedmont Upland Section is an area of rounded hills and flat-floored valleys devel­ Piedmont oped by weathering and erosion of schist, Section gneiss, metaquartzite, and other metamor­ phic rocks. In situ regolith includes weath­ Figure 1. Map showing area of the Piedmont ered rock and saprolite. Transported regolith Upland Section, Piedmont Province (black area) includes alluvium, colluvium, fluvial terrace in southeastern Pennsylvania. Small rectangle deposits, and anthropogenic deposits. within the Piedmont Upland Section and adjacent Weathered rock occurs almost everywhere area shows location of Figure 2. except where erosion has exposed unweath­ ered bedrock in valley bottoms. Thin colluvi­ (e.g., Custer, 1985 ; Hersh, 1963; Kunkle, 1963) um occurs discontinuously on hill tops and address the uppermostst part of the regolith as a side slopes while thicker colluvium occurs in material, but do not touch on its origin or histor­ heads of first-order drainage basins and in ical significance. This paper presents informa­ small valleys lacking perennial streams. Al­ tion obtained during recent mapping of regolith luvium is present in all valleys with perennial in southeastern Pennsylvania. streams. This regolith is the product of early The Pennsylvania Geological Survey started to middle Cenozoic weathering, middle to to investigate the bedrock geology of the PiPied­ late Cenozoic erosion, Pleistocene periglacial mont Upland Section of Lancaster County in erosion and deposition, and recent anthropo­ 1987. In 1989 this work was expanded in a co­ genic activity. operative project with the Maryland Geological Survey to map the surficial geology of the York INTRODUCTION 1: lOO,ODO-scale quadrangle (Fig. 2), an area of 32 1 :24,OOO-scale quadrangles in York, Lan­ Regolith includes all the unconsolidated ma­ caster, and Chester Counties, Pennsylvania and terial at the surface of Earth's crust,st, regardless Carroll, Baltimore, Harford, and Cecil Coun­ of its origin (Merrill, 1897). Regolith of diverse ties, Maryland. Twelve full and 6 partial character and origin covers much of the Pied­ 1 :24,OOO-scale quadrangles (Fig. 2) were mont Upland Section of the Piedmont Province mapped in Pennsylvania and the project termi­ in southeastern Pennsylvania (Fig. J), Until re­ nated upon completion of open-file reports cently this regolith received little attention from (Sevon, 1996). the geological community, Various soils reports

223 W.D.SEVON

.:: ot> <>.. /

CHESTER CO.

Figure 2. Index map showing that part of the York 1:100,000 quadrangle, Pennsylvania-Maryland, mapped and reported on herein. The York quadrangle is subdivided into 1:24,000-scale quadrangles whose names and open-file report numbers are in diagonal lettering.

BEDROCK GEOLOGY facies are dominated by quartz with smaller but abundant quantities of feldspar. Bedrock Other rocks include metabasalt, mica-chlo­ rite quartzite schist of the Marburg Schist, ser­ Bedrock in the Piedmont Upland Section in pentinite, Peach Bottom Slate, Cardiff York, Lancaster, and Chester Counties is mainly Conglomerate, metaquartzites of the Cambrianan schist, but a variety of other metamorphic rocks Chickies and Antietam Formations, phyllites occur. The Geologic Map of Pennsylvania and schists of the Cambrian Harpers Formation, (Berg and others, 1980) shows the schist as ei­ and gneiss. The character of all of these rocks, ther Wissahickon Formation or Peters Creek except for gneiss, is discussed in Stose and J 0- Formation, both of presumed lower Paleozoic nas (1939). These other rocks all have very age. Valentino (1994) indicates that schist north small areal distribution except for the Marburg of the Peters Creek Formation in the western Schist and the gneiss (Fig. 3). Piedmont should be termed Octoraro Formation rather than Wissahickon Formation. That termi­ Structure nology is followed here (Fig. 3). The Octoraro Formation consists of numer­ From a tectonic point of view, structure in the ous lithologically distinct members including Piedmont Upland is complex and involves mul­ pelitic schist, plagioclase-bearing schist, units tiple episodes of metamorphism and deforma­ of interlayered schist and metasandstone, and tion (Valentino, 1994). From a regolith point of phyllonite. All of these rocks contain moderate view, structure is relatively simple. Most of the to large amounts of muscovite and small to rocks are dominated by a well developed schis­ moderate amounts of quartz. tosity that generally trends 0600 ± 10° azimuth The Peters Creek Formation has three but locally may diverge considerably from that metasedimentary lithofacies: quartzose schist, orientation (Wise, 1970). This schistosity is graded metasandstone, and massive metasand­ considered to be parallel or subparallel to the stone (Valentino and Gates, 1995). The quart­ bedding of the pre-metamorphosed sedimenta­ zose schist consists of about equal parts of ry rocks. quartz, chlorite, and muscovite. The other litho- The schistosity dips south at angles generally

224 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

EXPLANATION e Cambrian and Ordovician M Marburg Formation W Wissah ickon Formation gn Gneiss m Marble carbonates o Octoraro Formation PB Peach Botto';' slate and s Serpentinite mv Metavolcanics Q Metaquartzites of the Cardiff conglomerate PC Peters Creek Formation Chickies, Antietam, and Harpers Formations Figure 3. Bedrock geologic map of the mapped area (from Berg and others, 1980). Axis of Tucquan antiform and contours of dip of foliation (dashed lines) modified from Wise (1970). greater than 30° in much of the area (Fig. 3). In uplands. The steepest slopes occur in the lower the north-central part of the area (Safe Harbor, reaches of tributaries to the Susquehanna River Conestoga, and Quarryville quadrangles in Fig. and along the Susquehanna River itself. 2) the dip of schistosity flattens and reverses di­ The Susquehanna River cuts through the up­ rection across the Tucquan antiform (Fig. 3). land in a gorge that is 120-150 m deep through Two other well developed but less prominent most of its length, but lessens to only 60 m deep schistosities occur. Fractures are abundant. Ser­ near the boundary between Pennsylvania and pentinite and gneiss are massive rocks that lack Maryland. All other drainage in the mapped ar­ the systematic planes described above. ea is to the Susquehanna River. Drainage pattern inland from the Susquehan­ GEOMORPHOLOGY na River is mainly dendritic (e.g., Muddy Creek in the Airville and Stewartstown quadrangles Terrain of the Piedmont Upland Section con­ [Fig. 4]). Trellis pattern occurs in the northern sists of rounded hills and narrow to broad, flat­ part of the Glen Rock quadrangle (Fig. 4) where floored valleys. Uplands are never absolutely alternations of rocks of different hardness paral­ flat, but some in Lancaster County have small lel the dominant schistosity. Many short reaches areas that are nearly flat. More than two thirds of streams throughout the mapped area trend of the landscape is gently sloping and undulat­ parallel to the plane of dominant schistosity ing to moderately sloping and rolling (Custer, (e.g., southwest quarter of the Gap quadrangle; 1985; Hersh, 1963; Kunkle, 1963). Less than 15 western quarter of the Wakefield quadrangle percent of the landscape is steeply sloping [Fig. 4]). (Custer, 1985; Hersh, 1963; Kunkle, 1963). Streams entering the Susquehanna River are Slopes are gentle in the headwaters of first-or­ entrenched in their valleys for a kilometer or der drainage basins and increase in steepness more upstream from their mouths. These gradually downstream as the valley becomes streams flow on bedrock in the entrenched well defined and deepens relative to adjacent reaches where there is generally no floodplain

225 W.D.SEVON

o 5 10 KM .," ".!!! Figure 4. Map of drainage pattern in part of the York 1:100,000 quadrangle. Stream names are: C.C. - Conowingo Creek; M.C. - Muddy Creek; W.R.O.C. - West Branch Octoraro Creek. Quadrangles referred to in text are: A - Airville; G - Gap; GR - Glen Rock; K - Kirkwood; S - Stewartstown; W - Wakefield.

and some to abundant exposure of bedrock strong visual impression of elevation accor­ along the valley walls. The entrenched reach dance with adjacent and distant uplands. In ad­ terminates upstream at a knickpoint. Upstream dition, there appears to be, in places, a from the knkkpoint there is a broad floodplain downward stairstepping of accordant levels. and little or no bedrock exposed within the val­ These aspects of accordance, which are more ley. Larger streams such as West Branch Octor­ visual than real, contributed to earlier interpre­ aro Creek in the Kirkwood quadrangle and tations of numerous peneplain levels (Knopf Conowingo Creek in the Wakefield quadrangle and Jonas, 1929). (Fig. 4) have additional knickpoints upstream from the lowermost one. Lengthy and well de­ REGOLITH veloped floodplain reaches separate each one of these additional knickpoints. Introduction Maximum elevation in the area is 318 m; minimum, 34 m. Elevation in about half the area Regolith in the Piedmont Upland Section of is between 183 and 213 m. The highest area east the mapped area comprises in situ and trans­ of the Susqehanna River is on the crest of the ported materials. In situ regolith consists of Tucquan antiform (Fig. 3); west of the Susque­ weathered bedrock (Graham and others, 1994) hanna River, on the drainage divide between and saprolite (Stolt and Baker, 1994). Trans­ north and south flowing drainage (Fig. 4). Local ported regolith consists of alluvium, colluvium, relief in York County is generally 60-90 m; in and anthropogenic deposits. Except for material Lancaster County, generally 30-60 m; in Ches­ present in fluvial terrace deposits along the Sus­ ter County, generally 30-50 m. The Piedmont quehanna River, all of the mapped regolith orig­ Upland is separated from the Piedmont Low­ inated within the Upland Section. Occasional land to the north by an abrupt, well defined, occurrences of high silt content in the upper­ steep slope that rises 50 m or more from the most part of soil profiles on uplands near the lowland to the upland. Susquehanna River probably indicate the pres­ Views from the tops of many uplands give a ence of locally derived loess (Pollack, 1992),

226 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

EXPLANATION N A Alluvium RU Upland rock residuum AC Alluvium and colluvium, RC Rock and colluvium t undivided , Continuous or discontinuous C Colluvium outcrop S Saprolite oLOCATION

Figure 5. Geologic map of the regolith in part of the Kirkwood quadrangle, Lancaster and Chester Counties, Pennsylvania (See Fig. 2 for location.). Contour interval is 20 feet. but the silt is a very minor component of the re­ lies sloping uplands and side slopes and is gen­ golith. Soils occur on all of the nonanthropo­ erally less weathered than upland rock genic regolith materials, but are not discussed residuum. Alluvium and colluvium are trans­ here (see Custer [1985], Hersh [1963], and ported regolith units. Alluvium and colluvium Kunkle, [1963] for soils information). Figure 5 undivided is a map unit utilized wherever both is an example of a map of the regolith. alluvium and colluvium occur in the same val­ Saprolite and upland rock residuum are in ley bottom, but cannot be differentiated at the situ regolith units on the map. The upland rock 1 :24,000 map scale. residuum is deeply weathered rock that is not weathered sufficiently to be classified as sapro­ lite and that underlies a relatively flat upland. Rock of the rock and colluvium map unit under-

227 W.D.SEVON

In Situ Regolith ing and stress-release fracturing caused by erosion (Ferguson, 1967; Wyrick and Borchers, Weathered Bedrock 1981). Weathered bedrock comprises all in situ rock Considerable variation occurs in bedrock­ that occurs between the surface (or saprolite or fragment quantity, size, and degree of weather­ an overlying transported regolith) and unweath­ ing. This variation is best seen in plowed fields. ered bedrock at depth. Not all weathered bed­ The presence of large, unweathered, rock frag­ rock is regolith. Only weathered bedrock that is ments indicates that unweathered bedrock is broken or breaks readily with application of near the surface. The presence of only small, minimal force is considered regolith. Chemical­ deeply weathered, rock fragments indicates that ly weathered bedrock that retains coherence and unweathered bedrock is not near the surface. resistance to breakup is not considered regolith. This di stinction is subjective and is best ob­ Table 1 indicates the depth to what water­ served in fields that have been plowed but lack well drillers consider unweathered bedrock in crops, have been rained upon one or more times the map area. The records from which the data since being plowed, and have continuous expo­ come are inadequate to indicate the nature of sure from upland top to valley bottom. the weathered-bedrock zone. A few outcrops Some plowed fields show considerable rock­ show that the upper part of this zone comprises fragment variation within very short distances, either bedrock that is broken or bedrock that is a few meters or less. Small areas with abundant, easily broken. The lower part probably com­ large, unweathered, rock fragments may occur prises bedrock that is chemically weathered to adjacent to areas with much smaller, more some extent, but not broken or easily broken. weathered, rock fragments or adjacent to mate­ Near-surface bedrock breaks along planes of rial interpreted as saprolite that has very few or foliation and fracture. This zone of broken bed­ no rock fragments. These rock-fragment varia­ rock may be several meters thick (Fig. 6). Foli­ tions usually occur in bands that parallel domi­ ation in the upper part of the broken-bedrock nant foliation. zone rotates to a downslope direction and a Mineral alteration of bedrock in the weath­ slope-parallel orientation. There may be a well­ ered-bedrock zone is variable, but has not been defined plane of detachment separating weath­ studied in the mapped area. Much of the bed­ ered-bedrock regolith from non-regolith weath­ rock is iron stained from weathering of iron­ ered bedrock. The amount of separation bearing minerals such as magnetite. The degree between broken pieces is variable but is gener­ of chemical alteration is not enough to produce ally in the range of a few millimeters to a few a saprolite but is enough to aid bedrock break­ centimeters. The size of the broken pieces is up. variable and is controlled by spacing of the Lithofacies and foliation control bedrock planes of foliation and fracture. Bedrock break­ weathering and saprolite development. Lithofa­ up results from physical and chemical weather­ cies within the schists can vary almost meter by Table 1. Thickness of regolith in the Piedmont meter (Valentino, unpublished data on file at the Upland section of part of York, Lancaster, and Pennsylvania Geological Survey, Harrisburg). Chester Counties. Consequently, it is common to have very weath­

I ering-susceptible lithofacies interspersed with Number i Standard R of weathering-resistant lithofacies and thin zones Bedrock i Meanl deviation ange . wells , 2 of weathered bedrock or saprolite adjacent to essentially unweathered bedrock (Fig. 7). In I Schist _ . 1 i 7 ; 0-69 !2864 ! Metaquartzite 13 9 : O~ 72 428 much of the mapped area, foliation dips south at Gneiss 13 --c--cc----+-2c-_-c- 6 i 28 greater than 30° (Fig. 3). In this area depth to 1 •• Depth to bedrock in meters. unweathered rock is generally greater than 10m 2 • Data from water well records on file at the Penn­ (Table 1), but unweathered rock and saprolite ; sylvania Geological Survey, Harrisburg, PA distribution and depth to unweathered bedrock --- distribution and depth to unweathered bedrock

228 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

Figure 6. Photograph of an outcrop of regolith composed of broken and weathered rock in Lancaster County. Regolith has slight separation of weathered rock along foliation planes, some rotation near the surface, and a hint of detachment from less weathered and unbroken bedrock in the lower part of the outcrop (at dashed line). Bedrock is schist of the Peters Creek Formation. Scale is divided into IO-cm intervals.

Figure 7. Photograph of an outcrop of unweathered bedrock (on left) adjacent to saprolite (on right) in Lancaster County. Bedrock is schist of the Peters Creek Formation. Foliation is dipping to the right (south). Scale is divided into IO-cm intervals.

are variable because of variations in bedrock face. Where foliation is parallel to the surface, lithofacies (Fig. 8). The relationship between water infiltration and subsequent rock weather­ bedrock lithofacies and degree of saprolite de­ ing is inhibited and depth of weathering is velopment has not been studied in this area. small. In the north-central part of the area where fo­ Two weathered rock units were used in map­ liation flattens across the Tucquan antiform ping to subdivide the large area of weathered (Fig. 3), unweathered rock is almost at the sur- rock that occurs in the Piedmont Upland. Up-

229 W.D.SEVON

ally absent in York County. Local, small occur­ rences of saprolite may occur anywhere, but are generally undetectable except by chance expo­ sure. Mappable saprolite occurs only on the highest uplands and is probably not more than a few meters thick. Unfortunately, data from wa­ ter-well drill holes (Table 1) is not adequate to permit discrimination of saprolite from weath­ ered bedrock. Plowed fields on saprolite are al­ most totall y devoid of rock fragments and those fragments that occur are small and deeply weathered. Surfaces generally devoid of rock Figure 8. Cross section of landscape (no scale) fragments and interpreted to be underlain by showing hypothetical variability of thickness of saprolite may have abundant fragments of vein weathered bedrock and saprolite as a function of quartz. Vein quartz is common, but not ubiqui­ foliation and lithofacies differences. tous in the Piedmont Upland area. Rock frag­ ments typical of weathered rock are found only land rock residuum comprises weathered rock a few meters in elevation below the upper sur­ that underlies relatively flat uplands but is not face of those few uplands underlain by saproli­ weathered sufficiently to be called saprolite. te. As indicated previously, saprolite may occur Most of the Piedmont Upland slopes are under­ adjacent to unweathered bedrock because of lain by rock that is variably weathered, but is differences in weathering susceptibility of not as weathered as upland rock residuum. It is schist lithofacies (Fig. 7). Narrow, foliation-par­ possible that this widespread weathered rock allel bands of saprolite occurring between larg­ unit could be subdivided into two units based er bands of weathered schist are sometimes partly on degree of weathering and partly on recognizable in plowed fields because the band slope position. However, availability of out­ of saprolite is significantly redder in color than crops and plowed fields were not sufficient to the adjacent weathered schist. allow such subdivision during this mapping Saprolite formed from metaquartzite is very project. uniform and is composed entirely of gray, quartz sand. Saprolite formed from schist is Saprolite variable in character depending on the parent Saprolite, as the term is used here, refers to schist. In the Octoraro Formation saprolite is material that "is isovolumetric with the underly­ mainly quartz and muscovite with occasional ing bedrock, as indicated by the retention of tex­ seams of vein quartz and is yellow brown to red­ ture and fabric of the parent material, and it dish in color. Rocks in the Peters Creek Forma­ exhibits gradational chemical and mineralogi­ tion are dominated by quartz; the associated cal changes of composition going from the par­ saprolites are generally gray and contain lots of ent to the geomorphic surface" (Pavich, 1985, p. quartz and some muscovite. Exposures of 308; see also Stolt and Baker, 1994). In addi­ saprolite in other rock types have not been ob­ tion, there has been little or no "movement of al­ served. teration products. Leaching has changed feldspars to clay minerals and oxidation of fer­ Transported Regolith rous iron to ferric iron has given the saprolite a Alluvium brownish color" (Carroll, 1970, p.p. 19-20). Sapr­ olites are typically soft and are easily dug with Alluvium isis material that has been transport­ a shovel or cut with a knife. ed and deposited by running water (Buol, Mappable (1 :24,000 scale) saprolite occurs 1994). Alluvium occurs throughout the mapped in Lancaster and Chester Counties, but is gener- area in the bottoms of valleys possessing peren-

230 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

Figure 9. Photograph of alluvium exposed along Conowingo Creek, northern Wakefield quadrangle, Lancaster County (See Fig. 4 for location of quadrangle). Measurement and description at vertical bar. Unit 1 is a gravel bar composed of platy fragments of schist (90 % j:) and vein quartz (10% j:). Pebbles are mostly in point contact and 0.5-4 cm in largest dimension. Platy fragments are imbricated. Inter­ stices are filled with clay, silt, and 2-5 mm quartz granules. Matrix is light to medium gray because of organic content. An additional 40 cm of gravel bar occurs below water level. Unit 2 is medium to dark gray, organic-rich silt and clay with scattered 2 mm- to 1 em-diameter quartz pebbles in the lower 10- 15 cm. Unit thickens laterally away from crest of gravel bar and changes to light gray and reddish yel­ low mottled silt and clay with a basal organic-rich zone that is gradational into the underlying gravel and a thin « 10 em) organic zone at the top. Unit 3 is brown, uniform, vertically-burrowed silt and clay with almost no sand or pebbles. No soil development occurs at the floodplain surface.

Figure 10. Photograph of a man-made outcrop of colluvium along the Conrail railroad line at Peters Creek in Lancaster County. Rock fragments are derived from schist of the Peters Creek Formation. Note irregular shape and random orientation of rock fragments in Unit A (lower) and slope-parallel orientation of platy rock fragments in Unit B (upper). C is one of several large blocks of schist that occur at the base of the deposit.

231 W.D.SEVON

Figure 11. Photograph of fine-grained colluvium overlying weathered slate of the Cambrian-age Chickies Formation in a temporary excavation near York in York County. Arrow points to slate that is bent by down-slope creep. Colluvium is derived from deeply weathered slate or saprolite farther ups­ lope. Most, if not all, of the exposed weathered slate is sufficiently broken and separated along planes of foliation to be called regolith. Slope is less than 5°. Scale is divided into 10-cm intervals.

Figure 12. Photograph of blocks of schist that comprise part of colluvium at the base of a typical steep bedrock slope in Lancaster County. Blocks are derived from the Peters Creek Formation. Scale is divided into 10-cm intervals. nial steams. The alluvium comprises deposits of um. the floodplains and stream channels. The flood­ Most exposures of alluvium show two con­con­ plains are a few to many tens of meters in width, trasting components: lower coarse-grained ma­ are quite flat, and have well defined changes in terial and upper fine-grained material (Fig. 9). slope gradient at their margins. In almost every The lower material is composed of schist frag­ valley the stream has eroded into the floodplain ments and/or pieces of vein quartz in a matrix of sediments to a depth of a meter or more. Expo­ sand, silt, and clay. Stratification and sorting are sures in cutbanks along these streams provide present and platy fragments are imbricated. the only available information about the alluvi- These coarse materials are generally capped by

232 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA a few to many centimeters of fine-grained sedi­ dent upon the nature of the parent material. Ma­ ment that is either light to dark gray throughout trix derived from metaquartzitemetaquartzite is mainly sand because of high organic content or is capped by with some silt. Matrix derived from schist is a dark organic zone, a presumed paleosol A-ho­ composed of granules, a moderate amount of rizon. This organic zone has a sharp upper sand and silt and a little clay. Small to large vari­ boundary. It is overlain by up to a meter of fine­ ations in matrix texture and color are common. Cb grained sediment that is brown in color, has Brown colluvium: high rock fragment content, low matrix very few or no rock fragments, little or no strat­ Content, abrupt base, occa$ional basal stonelines. ification, and no soil development. Clr Light red colluvium: 7.5YR5/6±, low rock fragment content, The data available indicate that the alluvium High matrix content, abrupt to transitional base, occasional basal stonelines. is seldom more than a few meters thick in most Cdr Dark red colluvium: 2.SYR4/8-5YR5/S, moderate to high rock valleys and is often little more than a meter fragment content, moderate matrix content, may have several thick. discrete red layers, abrupt base. Ps Pseudo-saprolite: color and mineralogic banding, finely Colluvium bedded, bedding parallels slope, abrupt base.

Colluvium is mass-transported, unconsoli- S Saprolite dated material (Buol, 1994) composed of a Rw Weathered rock poorly sorted to unsorted mixture of clay, silt, poorly sorted to unsorted mixture of clay, silt, R Unweathered rock sand, and rock fragments (Fig. 10). The rock Figure 13. Idealized stratigraphic sequence fragments are derived from local bedrock, are occurring in areas of colluvium. surrounded by a fine-grained matrix, are gener­ ally in contact with each other, and often com­ The primary stratigraphic sequence within prise the bulk of the colluvium. A vertical the colluvium in the mapped area is shown in sequence of colluvium may have abrupt chang­ Figure 13. Where observed in cross section es in matrix texture, rock-fragment content, and (generally in back-hoe pits), the boundaries be­ color (Pollack, 1992). tween units are sharp, the order of the sequence Rock fragments impart character to the col­ is invariable, and the various units sometimes luvium. Derived mainly from either schist or have stonelines at their boundaries. The three- quartzite in the mapped area, the fragments are dimensional continuity of colluvial units is not usually platy when only a few centimeters long known. However, observed cross-sections in but are irregular in shape when larger. The frag­ backhoe pits as close together as 15 m have no ments may have any orientation within the col­ correlation of specific colluvial units, Sequenc­ luvium (Fig. 10), but the platy fragments tend to es examined in many backhoe pits and other ex­ be aligned subparallel to the slope and often the posures (Pollack, 1992) indicate that any alignment gives the appearance of crude bed­ number of the stratigraphic units may be absent ding. The rock fragments are variably weath­ at a particular site. The lower red colluvium is ered depending upon the degree of weathering of particular interest because the parent material of the parent bedrock and the length of time in is not red. Pollack (1992) indicates that, except residence as colluvium. Rock fragments are for its color, the red unit lacks indicators of deep generally sparse to absent in colluvium derived soil development: i.e., clay films and well-de­ from saprolite or deeply weathered rock (Fig. veloped structure. Therefore, the lower red unit 11). Colluvium at the base of steep slopes may represent either material deeply weathered where unweathered bedrock is close to the sur­ prior to downslope transport and deposition or face is usually composed of blocks a meter or material that was transported, deposited, deeply more in at least one dimension (Figs. 10 and weathered, partly stripped, and then frost 12). The character and relative abundance of churned. clasts on the surface are invaluable aids to map­ Not all sequences of colluvium fit the simple ping. stratigraphy in Figure 13. Some sequences have The matrix material is variable, again depen- more than four discrete colluvial units. These

233 W.D.SEVON

Figure 14. Block diagram showing variability in occurrence and thickness of colluvium in different landscape positions. are distinguished by sharp to transitional Colluvium is usually less than 2 m thick except boundaries, changes in matrix texture, rock­ in centers of small fIrst-order drainage basins fragment content, and color. Within the numer­ lacking perennial streams. However, thick col­ ous sequences containing many thin, discrete luvium may occur almost anywhere on the land­ units, no consistent vertical stratigraphy exists scape. beyond that shown in Figure 13. Pseudo-saprolite Ice wedge casts and involutions, structures interpreted to be periglacial in origin (Pollack, Included within the category of colluvium is 1992), occur in the colluvium but are not often a deposit different from the colluvium de­ seen because of lack of good exposures. Similar scribed above. This material is composed of structures are known from many places else­ quartz and muscovite grains, is very evenly bed­ where in Pennsylvania (Ciolkosz and others, ded at the millimeter scale, has striking alterna­ 1986). These structures occur in interfluve areas tions of color, and has bedding that is similar in and are formed mainly in the lower red colluvi­ appearance to layering in saprolite. The deposit, um (Fig. 13). where present, is always at the base of the col­ Colluvium is widespread within the mapped luvial sequence (Fig. 13) and rests on a surface area. It may be found anywhere except on near­ that truncates either saprolite or bedrock. Bed­ ly vertical slopes and broad floodplains. Its ding of the deposit is parallel to subparallel to thickness is variable and unpredictable within slope. The material is very friable and well sort­ the same landscape element (interfluve, shoul­ ed within individual layers. The deposit is not der, backs lope, and footslope), but predictably known to be more than a few tens of centimeters thinner in divergent (convex) slope positions thick. Because of its appearance, this material and thicker in convergent (concave) slope posi­ can be easily confused with saprolite in small tions (Pollack, 1992). Colluvium is absent at the isolated outcrops. However, observed saprolite slope shoulder where bedrock is near or at the in the area is not as finely layered and musco­ surface. Colluvium generally thickens downs­ vite in the saprolite does not have the appear­ lope from the shoulder and is typically thickest ance of being discrete, detrital grains. at the base of the footslope. Figure 14 is a hypo­ Observation of limited exposures indicates that thetical diagram showing colluvium variability. this is saprolite-derived material that has been

234 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA transported from its original position by creep Epoch within the last 1.8 Ma. and has suffered minimal disturbance during Several exposures in stream valleys tributary the process, which is why it resembles saprolite to the Susquehanna River show gravels com­ so closely. posed of quartz and schist fragments. These gravels are a few centimeters thick and occur in Alluvium and colluvium undivided positions on the landscape above the modern Alluvium and colluvium undivided is a unit floodplain level. The gravels are presumably of mapping convenience. It occurs in valleys fluvial terrace deposits. However, they have not that are too narrow to allow map separation been mapped as such because there is no asso­ (1:24,000 scale) of the two units. Limited expo­ ciated terrace morphology, the deposits are bur­ sures show that stratified alluvium is laterally ied beneath colluvium, and they are less than 2 interbedded with unstratified colluvium. In m thick. some of these valleys colluvial slopes from ad­ Anthropogenic deposits jacent valley sides meet along limited stretches in the valley center and no floodplain exists Most regolith materials of anthropogenic or­ even though a perennial stream is present. The igin in the mapped area are the result of erosion general character of the materials appears to be of soil since settlement and land clearing (Trim­ the same as described above for alluvium and ble, 1974). Most of this material is included in colluvium. Distinct stratigraphic units in the mapped deposits of alluvium and colluvium. colluvium, such as those in Figure 13, were not Small, unmapped deposits of this type include observed. the following: (1) The upper reaches of first-or­ der drainage basins often have fence rows nor­ Fluvial terrace deposits mal to valley length. Accumulations of eroded Fluvial terrace deposits exist in the mapped sediment on the upslope side of the fence row area along the Susquehanna River, but have not are often a half meter or more thick. (2) Small, been mapped because they are less than 2 mm fan-shaped deposits of eroded material are often thick. These deposits have been studied in detail present at the base of slopes adjacent to flood­ by Pazzaglia and Gardner (1993) and their in­ plains. Here, soil eroded from upslope fields has terpretations are critical to the discussion of been channeled by convergent slopes to the base geologic history presented below. of the sideslope. The bulk of this material lies Although mappable (l :24,000 scale) fluvial on floodplain alluvium and is mapped as alluvi­ terrace deposits occur at several different levels um. (3) The fine-grained, brown alluvium that outside the Piedmont Upland Section (Engel lies above the buried organic zone in flood­ and others, 1996), deposits of each level are plains of all sizes is sediment eroded from the generally absent within the gorge cut through landscape since land clearing and the start of the upland by the Susquehanna River. The cultivation. (4) Additional mappable (1 :24,000 steepness of the gorge walls has prevented pres­ scale) anthropogenic materials include solid­ ervation of these deposits except in a few places waste landfills and artificial fill used extensive­ where rock-cut straths occur. Thin fluvial ter­ ly to elevate roadways. race deposits are preserved on the uplands adja­ In urban areas where a lot of development cent to and within a kilometer of the has occurred, much of the landscape can be Susquehanna River. Materials in these upper termed disturbed land. Here the regolith mate­ terrace deposits are primarily resistant litholo­ rials have been removed, rearranged, and relo­ gies (quartz, quartzite, and sandstone) derived cated in a variety of ways. However, a few years from outside the Piedmont upland. The lower after disturbance, construction, and landscaping terraces contain lithologies that can only have are completed, it is difficult to recognize the been derived from Grenville rocks in Canada type and amount of disturbance unless refer­ and were brought into the upper Susquehanna ence is made to pre-disturbance aerial photo­ River basin by glaciers during the Pleistocene graphs. These areas of disturbed land have not

235 W.D.SEVON been mapped. Eocene (Wing and Greenwood, 1994). Erosion of clastic material was at a minimum and chem­ GEOLOGIC HISTORY ical erosion was at a maximum throughout this period of time. Mesozoic Geologists speculate about the appearance of the landscape in the Piedmont Upland Section There is little real data about the history of of York, Lancaster, and Chester Counties during the Piedmont Upland Section during the Meso­ early and middle Cenozoic time. Pazzaglia and zoic. Up to 12 krn of material have been eroded Gardner (1993) investigated the fluvial terraces from the Piedmont since the end of the Al­ of the Susquehanna River and proposed that the leghanian orogeny about 260 Ma (Kohn and highest fluvial terrace, (unit Tgl) at 140 m others, 1993). The Cenozoic history discussed above the present Susquehanna River channel below requires that most of the 12 km thickness in the upland area, was deposited during the late be eroded during the Mesozoic. Drainage was early to early middle Miocene (-20-15 Ma). to the northwest during at least the early part of Tributaries would have been graded to the Sus­ the Mesozoic (Sevon, 1994). quehanna River at that level. I hypothesize that The Piedmont uplands contributed sediment local relief in these tributary drainage basins to the Mesozoic basin that lay to the northwest would have been no greater than today, and may during the late Triassic and early Jurassic have been less, perhaps 50 m or less. The land­ (Glaeser, 1966). There is no absolute evidence forms may have been similar to those of today, to indicate when northwest-flowing drainage but the preceding extended period of uninter­ reversed and the Susquehanna River began to rupted erosion (>40 my) more likely produced a flow from the interior of Pennsylvania to the At­ landscape of more subdued topography with lantic Ocean. However, isopach maps of allos­ broader valleys and gentler slopes (a pene­ tratigraphic units in the Salisbury Embayment, plain?). The lower reaches of tributaries to the Baltimore Trough (Poag and Sevon, 1989; Po­ Susquehanna River would not have been in­ ag, 1992) show sediment accumulations proba­ cised as they are today. I assume that the extend­ bly attributable to the Susquehanna River as ed period of chemical erosion produced a land early as the start of the Cretaceous (144 Ma). surface underlain by thick saprolite and deeply These isopach maps indicate that all sediment weathered rock (Fig. 15:1). sources between Cape Cod (Massachusetts) and the James River (Virginia) provided continuous Middle Miocene-present but fluctuating quantities of sediment to the Baltimore Trough throughout the Cretaceous. The offshore record (Poag and Sevon, 1989; Presumably the Piedmont Upland Section con­ Poag, 1992) indicates that starting in the middle tributed sediment to the Susquehanna River Miocene large quantities of clastic sediment once its present course was established. were eroded from eastern North America. The Susquehanna River incised to within 40 m of Paleocene-early Miocene the present river channel level in the Piedmont Upland (Pazzaglia and Gardner, 1993) by about Poag and Sevon (1989) and Poag (1992) in­ the start of the Pleistocene (1.8 Ma). Tributaries dicate that from the end of the Cretaceous were graded to this new level and headward ero­ through the early Miocene, very little clastic sion carved the basic form of today's landscape sediment was deposited in the Baltimore (Fig. 15:2,3). Some of the saprolite and weath­ Trough by any of the contributing drainage sys­ ered rock formed during the preceding period of tems. Climate in eastern Pennsylvania during weathering was preserved on uplands, but much this time was at least as warm and wet as today. of that material was eroded. Valleys with broad Part of the time the climate was probably warm­ floodplains developed when streams estab­ er and wetter than today, particularly during the lished equilibrium profiles.

236 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

M Figure 15. Cross sections illus­ (AMSU trating a generalized model of landscape evolution and regolith development in the Piedmont Upland Section, York, Lancaster, and Chester Counties, Pennsyl­ vania prior to settlement in the 18th century. 1. A low-relief, ero­ sional surface was developed by

M physical erosion prior to the mid­ dle Miocene. Chemical weather­ ing produced thick saprolite and weathered rock. 2. Erosion start­ ing inin the Middle Miocene caused entrenchment of the Susque­ hanna River that, in turn, rejuve­ nated erosion by streams tributary to the Susquehanna River. Headward erosion incised the tributaries and caused ero­ sionallowering of the uplands. 3. By the start of the Pleistocene the tributary streams had attained equilibrium gradients, widened their valleys, and deposited allu­ vium on the floodplain. Slopes and uplands suffered minimal further erosion. 4. Pleistocene periglacial activity moved mate­ rial downslope and deposited it as colluvium. Upland tops were lowered. Some sediment was transported out of the area via streams; some was stored on floodplains. 5. Pleistocene lower­ ing of base level caused stream incision in the lower reaches of tributaries to the Susquehanna River, which in turn caused destruction of the floodplain, removal of some colluvium, and exposure of unweathered bed­ rock. AMSL = Above mean sea level.

100 200 300 400 500M

237 W.D.SEVON

Northeastern and northwestern Pennsylvania equal across the landscape during each of the experienced four documented glaciations dur­ multiple intervals of colluviation, and that any ing the Pleistocene: late Wisconsinan (Crowl or all (except the most recent) of the discrete and Sevon, 1980); Late Illinoian (oxygen iso­ colluviums could have been removed, dis­ tope stage 6) (Gardner and others, 1994); pre-Il­ turbed, or left undisturbed during a subsequent linoian (pre-Illinoian F or G of Richmond and periglacial episode. I suggest also that the red Fullerton, 1986) (Gardner and others, 1994); color of the oldest colluvium (Fig. 13) derives and an older glaciation of unknown age (White from interglacial weathering that followed a and others, 1969). Braun (1989) argues that four glacial interval that occurred more than 770,000 more glaciations, undocumented in Pennsylva­ years ago (Gardner and others, 1994). Weather­ nia, would also have affected Pennsylvania dur­ ing of comparable degree and color occurs on ing the past 850,000 years. During each of these old colluvium deposited elsewhere in Pennsyl­ glaciations the nonglaciated part of Pennsylva­ vania (Hoover and Ciolkosz, 1988; Ciolkosz nia was subject to a periglacial environment that and others, 1990; Waltman and others, 1990). profoundly affected the landscape. Soil development on the uppermost brown col­ Watts (1979) indicates that during these gla­ luvium (Fig. 13) is comparable to that on till cial intervals most of nonglaciated Pennsylva­ and other materials that were deposited in Penn­ nia was tundra and that continuous to sylvania during the late Wisconsinan (Ciolkosz discontinuous permafrost was present. Other and others, 1979). climatic modeling (Kutzback, 1987; Woodcock Base level dropped as the Susquehanna River and Wells, 1990) place the Piedmont uplands in eroded downward during the Pleistocene glacial a climate that was marginal for permafrost. epoch (Pazzaglia and Gardner, 1993) and Gardner and others (1991) suggest that perma­ knickpoints moved up Susquehanna River trib­ frost existed in parts of Pennsylvania only dur­ utaries. This caused incision of the lower reach­ ing glacial maximums, but that a vigorous es of these tributaries, erosion of some of the periglacial climate was present during both the colluvial deposits, and exposure of unweath­ waxing and waning phases of glaciation. Nu­ ered bedrock (Fig. 15:5). Coarse-grained alluvi­ merous observed periglacial features (Ciolkosz um was deposited upstream from the and others, 1986) support the former existence knickpoints while finer-grained materials were of periglaciation in Pennsylvania. Some of carried out of the drainage basins and deposited these features may be interpreted to indicate the elsewhere. presence of permafrost. Following the last glaciation, temperatures Intense freeze-thaw associated with perigla­ and precipitation fluctuated but gradually in­ ciation caused considerable breakup of both creased and Pennsylvania was revegetated weathered and unweathered rock. In addition, (Webb and others, 1993). That vegetation inhib­ solifluction moved unconsolidated material ited erosion of clastic material and the land­ from higher to lower slope positions (Fig. 15:4). scape remained relatively undisturbed until This material, the widespread colluvium, tells a about 300 years ago when European immigra­ story of multiple events through its stratigraphy. tion commenced. Subsequent land clearing and The four-part stratigraphy in the colluvium cultivation created an erosion-susceptible land­ (Fig. 13) suggests deposition during four glacial scape. Much of the soil eroded from this land­ intervals, but there is no age-dating evidence to scape is stored within the drainageways of the support this interpretation. Those sequences Piedmont Uplands, particularly on the flood­ that possess more than four stratigraphic units plains (Trimble, 1983). The fine-grained alluvi­ may reflect a better preservation of colluvial um above the buried organic zone is interpreted units formed during the eight probable perigla­ to be the result of post-settlement deposition cial episodes that affected Pennsylvania (Gard­ (Trimble, 1974). Changes in land use during the ner and others, 1991). latter half of this century have reduced the I suggest that erosion and deposition was un- amount of erosion and resultant sediment load

238 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA in streams. Consequently, streams are now Ciolkosz, Emery Cleaves, Thomas Gardner, eroding their channels. More recent anthropo­ Milan Pavich, Frank Pazzaglia, Jon Pollack, genic activities have added artificial deposits of and James Reger for helpful discussions in the various kinds to the landscape. field. Rodger Faill, Donald Hoskins, and Jon In­ ners provided manuscript review at the Pennsyl­ SUMMARY vania Geological Survey. Hugh H. Mills and Van Williams provided additional review. I ac­ The Piedmont Upland Section in southeast­ cept full responsibility for the interpretations ern Pennsylvania has undergone weathering made. and erosion since the end of the Alleghanian orogeny about 260 Ma. A long period of mini­ REFERENCES CITED mal physical erosion accompanied by maxi­ Berg, T. M., and 8 others, 1980, Geologic map of Pennsyl­ mum chemical erosion extended from the late vania: Pennsylvania Geological Survey, 4th ser., Map I, Mesozoic to the middle Miocene. Deep weath­ I :250,000 scale. ering during this interval produced two mappa­ Buol, S. w., 1994, Saprolite-regolith taxonomy-an approx­ ble in situ regolith units, weathered rock and the imation, in Cremeens, D. L, Brown, R. B., and Hud­ dleston, J. H., eds., Whole regolith pedology: Madison, end product of rock weathering, saprolite. Phys­ Wisconsin, Soil Science Society of America Special ical erosion commencing in the middle Mi­ Publication No. 34, p. 119-132. ocene produced the basic form of the landscape Braun, D. D., 1989, Glacial and periglacial erosion of the that exists today. This erosion left remnants of Appalachians, in Gardner, T. W., and Sevon, W. D., eds., saprolite and weathered rock beneath uplands Appalachian geomorphology: Geomorphology, v. 2, p. 233-256. and exposed unweathered rock in valley bot­ Carroll, D., 1970, Rock weathering: New York, Plenum toms. Weathered rock underlies side slopes ev­ Press, 203 p. erywhere and is the most areally extensive part Ciolkosz, E. J., Peterson, G. W., Cunningham, R. L., and of the in situ regolith. Weathered and unweath­ Matelski, R. P., 1979, Soils developed from colluvium ered rock materials were moved from higher to in the Ridge and Valley area of Pennsylvania: Soil Sci­ ence, v. 128, p. 153-162. lower slope positions during Pleistocene peri­ Ciolkosz, E. J., Cronce, R. C., and Sevon, W. D., 1986, Peri­ glacial episodes to produce colluvium, the most glacial features in Pennsylvania: University Park, abundant form of transported regolith in the Agronomy Department, The Pennsylvania State Uni­ Piedmont Upland Section. The colluvium has versity, Agronomy Series Number 92, 15 p. variable texture and stratigraphy produced by Ciolkosz, E. J., Carter, B. J., Hoover, M. T., Cronce, R. C., Waltman, W. J., and Dobos, R. R., 1990, Genesis of multiple peri glacially-driven movements of lo­ soils and landscapes in the Ridge and Valley province cally derived material. Alluvium composed of of central Pennsylvania: Geomorphology, v. 3, p. 245- locally derived material was deposited during 261. the Pleistocene and also after the land was Crowl, G. H., and Sevon, W. D., 1980, Glacial border depos­ cleared following settlement in the 18th and its of late Wisconsinan age in northeastern Pennsylva­ nia: Pennsylvania Geological Survey, 4th ser., General 19th centuries. Artificial fill associated with Geology Report G 71 , 68 p. construction and solid waste add to the comple­ Custer, B. H., 1985, Soil survey of Lancaster County, Penn­ ment of regolith materials. sylvania: U. S. Department of Agriculture, Soil Conser­ vation Service, 152 p. ACKNOWLEDGMENTS Engel, S. A., Gardner, T. w., and Ciolkosz, E. J., 1996, Qua­ ternary soil chronosequences on terraces of the Susque­ hanna River, Pennsylvania: Geomorphology, v. 17, p. This mapping project received partial fund­ 273-294. ing from the U. S. Geological Survey through Ferguson, H. F., 1967, Valley stress relief in the Allegheny the COGEOMAP program. Funding to Penn­ Plateau: Association of Engineering Geologists Bulle­ sylvania was from September 1989 to Septem­ tin, v. 4, p. 63-68. Gardner, T. w., Ritter, J. B., Shuman, C. A., Bell, J. C., ber 1992 (Contract Agreement Numbers 14-08- Sasowsky, K. c., and Pinter, N., 1991, A periglacial 0001-A0661, 14-08-0001-A0809, and 14-08- stratified slope deposit in the Valley and Ridge province 000l-A0870). I thank Duane Braun, Edward of central Pennsylvania, USA: sedimentology, stratig-

239 W.D.SEVON

raphy, and geomorphic evolution: Pennafrost and Peri­ sedimentary deposits of the U. S. middle Atlantic Con­ glacial Processes, v, 2, p, 141-162. tinentalal Margin, in Gardner, T. W., and Sevon, W. D., Gardner, T. W., Sasowsky, r. D., and Schmidt, V. A., 1994, eds., Appalachian geomorphology: Geomorphology, v. Reversed-polarity glacial sediments and revised glacial 2, p. 119-157. chronology, Westst Branch Susquehanna River valley, Pollack, J., 1992, Pedo-geomorphology of the Pennsylvania central Pennsylvania: Quaternary Research, v. 42, p. Piedmont [M.Sc. thesis]: University Park, The Pennsyl­ 131-135. vania State University, 294 p. Glaeser, J. D., 1966, Provenance, dispersal, and depositional Richmond, G. M., and Fullerton, D. S., 1986, Summation of environments of Triassic sediments in the Newark-Get­ Quaternary glaciations in the United States of America, tysburg basin: Pennsylvania Geological Survey, 4th in Richmond, G.G. M., and Fullerton, D. S., eds.,., Quater­ ser., General Geology Report G 43, 168 p. nary glaciations in the United States: Quaternary Sci­ Graham, R. c., Tice, K. R., and Guertal, W R., 1994, The ence Reviews, v. 5, p. 183-196. pedologic nature of weathered rock:, in Cremeens, D. Sevon, W. D., 1994, Pennsylvania: battleground of drainage L., Brown, R.R. B., and Huddleston, J. H., eds., Whole change: Pennsylvania Geology, v. 24, no. 4,4, p. 2-8. regolith pedology: Madison, Wisconsin, Soil Science Sevon, W D., 1996, Surficial geology of the Airville, Con­ Society of America Special Publication No. 34, p.p. 21- estoga, Gap, Glen Rock, Holtwood, Kirkwood, Quar­ 40. ryville, Red Lion, Safe Harbor, Stewartstown, Hersh, D. M., 1963, Soil survey of York County, Pennsylva­ Wakefield, and York quadrangles and the Pennsylvania nia: U. S. Department of Agriculture, Soil Conservation part of the Conowingo Dam, Delta, Fawn Grove, New Service, 159 p. Freedom, Norrisville, and Rising Sun quadrangles in Hoover, M. T., and Ciolkosz, E. J., 1988, Colluvial soil par­ York, Lancaster, and Chester Counties, Pennsylvania: ent material relationships in the Ridge and Valley Phys­ Pennsylvania Geological Survey, 4th ser., Open-file iographic Province of Pennsylvania: Soil Science, v. Reports 96-01 through 96-18, 18 maps, 1:24,000 scale, 145, p. 163-172. text 22 p. Knopf, E. B., and Jonas, A. I., 1929, Geology of the McCalis Stolt, M. H., and Baker, J. c., 1994, Strategies for studying Ferry-Quarryville district, Pennsylvania: U. S. Geolog­ saprolite and saprolite genesis, in Cremeens, D. L., ical Survey Bulletin 799, 156 p. Brown, R.R. B., and Huddleston, J. H ., eds, Whole Kohn, B. P. , Wagner, M. E., Lutz, T.T. M., and Organist,st, G., regolith pedology: Madison, Wisconsin, Soil Science 1993, Anomalous Mesozoic thermal regime, Central Society of America Specialal Publication No. 34, p. 1-19. Appalachian Piedmont: evidence from sphene and zir­ Stose, G. W., and Jonas, A. 1., 1939, Geology and mineral con fission-track dating: Journalal of Geology, v.v. 10 I , p.p. resources of York County, Pennsylvania: Pennsylvania 779-794. Geological Survey, 4th ser., County Report 67, 199 p. Kunkle, W M ., 1963, Soil survey of Chester and Delaware Trimble, S. W., 1974, Man-induced soil erosion on the Counties, Pennsylvania: U. S. Department of Agricul­ southern Piedmont 1700-1970: Soil Conservation Soci­ ture, Soil Conservation Service, 124 p. ety of America, 180 p. Kutzback, J. E., 1987, Model simulations of the climatic pat­ Trimble, S. W, 1983, A sediment budget for Coon Creek tern during deglaciation of North America, in Ruddi­ basin in the driftless area, Wisconsin, 1853-1977: man, W. F. , and Wright, H. E., Jr., eds., North America American Journal of Science, v. 263, p. 454-474. and adjacent oceans during the last deglaciation: Boul­ Valentino, D. w., 1994, Lithofacies and defonnation history der, Colorado, Geological Society of America, Geology of the Octoraro Formation and the relationship to the of North America, v. K-3, p. 425-446. Pleasant Grove-Huntingdon Valley shear zone, in Fain, Merrill, G. P. , 1897, A treatise on rocks, rock-weathering R. T. , and Sevon, W. D., eds., Various aspects of Pied­ and soils: New York, Macmillan,an, p. 299-300. mont geology in Lancaster and Chester Counties, Penn­ Pavich, M. J., 1985, Appalachian Piedmont morphogenesis: sylvania: Annual Field Conference of Pennsylvania weathering, erosion, and Cenozoic uplift, in Morisawa, Geologists, 59th, Lancaster, Guidebook, p. 25-34. M., and Hack, J.J. T. , eds., Tectonic geomorphology: Valentino, D. W., and Gates, A. E., 1995, Iapetan rift-related Boston, Allen and Unwin, p.p. 299-319. turbidite-fan deposits from the central Appalachian pazzaglia, F. J., and Gardner, T. W. , 1993, Fluvial terraces Piedmont: American Journal of Science, v. 295, p. 78- of the lower Susquehanna River: Geomorphology, v. 8, 97. p.83-ll3. Watts, W. A., 1979, Late Quaternary vegetation of central Poag, C. W., 1992, U. S. middle Atlantic continental rise: Appalachia and the New Jersey coastal plain: Ecologi­ provenance, dispersal, and deposition of Jurassicic to cal Monographs, v. 49, p.p. 427-469. Quaternary sediments, in Poag, C.C. W. , and deGracian­ Waltman, W. J. , Cunningham, R.R. L., and Ciolkosz, E. J.,J., sky, P. c., eds., Geologic evolution of Atlantic continen­ 1990, Stratigraphy and parent material relationships of tal rises: New York, Van Nostrand Reinhold, p. 100- red substratum soils on the Allegheny Plateau: Soil Sci­ 156. ence Society of America Journal, v. 54, p. 1049-1057. Poag, C. W , and Sevon,n, W D., 1989, A record of Appala­ Webb, T., III, Bartlein, P. J., Harrison, S. P., and Anderson, chian denudation in postrift Mesozoic and Cenozoic K.K. H., 1993, Vegetation, lake levels, and climate in east-

240 REGOLITH IN THE PIEDMONT UPLAND SECTION, SOUTHEASTERN PENNSYLVANIA

em North America for the past 18,000 years, in Wright, H, E., Jr., Kutzbach, 1. E., Webb, T., III, Ruddiman, W. F., Street-Perrott, F. A., and Bartlein, P. J., eds., Global climates since the last glacial maximum: Minneapolis, University of Minnesota Press, p. 415-467. Wing, S. L., and Greenwood, D. R., 1994, Fossils and fossil climate: the case for equable continental interiors in the Eocene, in Allen, J. R. L., Hoskins, B. J., Sellwood, B. W., Spicer, R. A., and Valdes, P. J., eds., Palaeoclimates and their modelling: London, Chapman and Hall, p. 35- 44. Wise, D. U., 1970, Multiple deformation, geosynclinal tran­ sitions and the Martic problem in Pennsylvania, in Fisher, G. W., Pettijohn, F. J., Reed, J. C, Jr., and Weaver, K. N., eds., Studies of Appalachian geology: New York, Interscience Publishers, p. 317-333. White, G. w., Totten, S. M., and Gross, D. L., 1969, Pleis­ tocene stratigraphy of northwestern Pennsylvania: Pennsylvania Geological Survey, 4th ser., General Geology Report G 55, 88 p. Woodcock, D. w., and Wells, P. v., 1990, Full-glacial sum­ mer temperatures in eastern North America as inferred from Wisconsinan vegetational zonation: Palaeogeog­ raphy, Palaeoclimatology, Palaeoecology, v. 79, p. 305- 312. Wyrick, G. G., and Borchers, J. W., 1981, Hydrologic effects of stress-relief fracturing in an Appalachian valley: U. S. Geological Survey Water-Supply Paper 2177,51 p.

241